[stdlib] Introduce availability macros

[lorentey]

Define the following availability macros throughout all Swift libraries and tests in this repository:

SwiftStdlib 5.0:macOS 10.14.4, iOS 12.2, watchOS 5.2, tvOS 12.2
SwiftStdlib 5.1:macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0
SwiftStdlib 5.2:macOS 10.15.4, iOS 13.4, watchOS 6.2, tvOS 13.4
SwiftStdlib 5.3:macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0
SwiftStdlib 5.4:macOS 11.3, iOS 14.5, watchOS 7.4, tvOS 14.5
SwiftStdlib 5.5:macOS 12.0, iOS 15.0, watchOS 8.0, tvOS 15.0
SwiftStdlib 5.6:macOS 9999, iOS 9999, watchOS 9999, tvOS 9999
SwiftStdlib 9999:macOS 9999, iOS 9999, watchOS 9999, tvOS 9999

These correspond to previous Swift Stdlib releases, in addition to the "5.6" release that we're currently working on, and the a placeholder "9999" release that we can use in place of an unknown future Swift release.

As part of this, we need to replace the pre-existing SwiftStdlib 5.5 macro defined in the _Concurrency module with the correct SwiftStdlib 5.1, so that its expansion matches our release history. (The concurrency runtime now deploys back to macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, which corresponds to the 5.1 release of the stdlib. Before this PR, this was reflected in the expansion of SwiftStdlib 5.5, but not its name.)

The new module _Distributed also defines SwiftStdlib 5.5, but its declarations need to have availability corresponding to the future Swift 5.6 release -- so this PR replaces it with SwiftStdlib 5.6.

To keep this PR (relatively) small, it does not include changes necessary to adopt these macros in existing stdlib code. (Beyond cleaning up the _Concurrency vs _Distributed situation.)

[lorentey]

@swift-ci test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 4795690

[lorentey]

Fascinating:

15:10:18 
/Users/buildnode/jenkins/workspace/swift-PR-macos/branch-main/swift/stdlib/public/Distributed/DistributedActor.swift:38:25: error: 'Identifiable' is only available in iOS 13 or newer
15:10:18     AnyActor, Sendable, Identifiable, Hashable, Codable {
15:10:18                         ^

The code is:

@available(SwiftStdlib 5.1, *)
public protocol DistributedActor:
    AnyActor, Sendable, Identifiable, Hashable, Codable {
    ...
}

AFAICT the Distributed module does not define any availability macros, so both SwiftStdlib 5.5 and SwiftStdlib 5.1 currently ought to resolve to @available(*). But then why would only this PR trigger this error? 🤔

@ktoso How does SwiftStdlib 5.5 work in this module?

[ktoso]

Discussed offline: the thing is defined in Distributed/CMakeLists.txt: -Xfrontend "SwiftStdlib 5.5:macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0", so we can keep those or change those in the future -- as the "5.5" is a bit of a lie anyway, this does not ship in 5.5.

[ktoso]

LGTM, Distributed should likely be really defined for 9999 so maybe you can do this? Thanks !

[lorentey]

Yep, I accidentally removed the SwiftStdlib 5.5 definition from CMakeLists.txt rather than updating it. 🤦‍♂️

The latest commit (temporarily) restores it and updates everything in _Distributed to come with SwiftStdlib 5.6 availability -- which currently resolves to 9999, sadly.

[lorentey]

@swift-ci test

[lorentey]

(The restoration is temporary as all these SwiftStdlib definitions (and more) will get moved to the top-level CMakeLists.txt soon.)

[lorentey]

Ugh, there will be a couple of test failures at least, as the tests only see SwiftStdlib 5.1 at the moment.)

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 5e78c3b

[lorentey]

Yep, as expected:

C:\Users\swift-ci\jenkins\workspace\swift-PR-windows\swift\test\Distributed\distributed_actor_resolve.swift:7:24: error: unexpected error produced: reference to undefined version '5.6' for availability macro 'SwiftStdlib'

@available(SwiftStdlib 5.6, *)

                       ^

[xymus]

This looks good! Thanks for refactoring the macros definition, it's much cleaner.

[lorentey]

The Windows build timed out.

[lorentey]

lit.py: /Users/buildnode/jenkins/workspace/swift-PR-macos-smoke-test/branch-main/llvm-project/llvm/utils/lit/lit/TestingConfig.py:102: fatal: unable to parse config file '/Users/buildnode/jenkins/workspace/swift-PR-macos-smoke-test/branch-main/swift/test/lit.cfg', traceback: Traceback (most recent call last):
  File "/Users/buildnode/jenkins/workspace/swift-PR-macos-smoke-test/branch-main/llvm-project/llvm/utils/lit/lit/TestingConfig.py", line 91, in load_from_path
    exec(compile(data, path, 'exec'), cfg_globals, None)
  File "/Users/buildnode/jenkins/workspace/swift-PR-macos-smoke-test/branch-main/swift/test/lit.cfg", line 435, in <module>
    for macro in lit_config.params.get('availability_macros').split(";"):
AttributeError: 'NoneType' object has no attribute 'split'

/Users/buildnode/jenkins/workspace/swift-PR-macos-smoke-test/branch-main/swift-driver/Tests/SwiftDriverTests/IntegrationTests.swift:241: error: -[SwiftDriverTests.IntegrationTests testLitSymbolGraphFrontendTest] : XCTAssertEqual failed: ("terminated(code: 2)") is not equal to ("terminated(code: 0)")
Test Case '-[SwiftDriverTests.IntegrationTests testLitSymbolGraphFrontendTest]' failed (2.502 seconds).

D'oh

[lorentey]

@swift-ci test